1. Field of the Invention
The present invention relates to a distance measuring apparatus and to a method for measuring the distance from the apparatus to an object by imaging reflected light of laser light emitted from the apparatus, and then referring to a positional relationship between the light emission position and the image position.
2. Description of the Related Art
Recently, CCD (Charged Coupled Device) cameras and computer image processing techniques have been improved, and accordingly, three-dimensional measurement methods using images have become common. An example of such three-dimensional measurement methods using a CCD camera and computer image processing is a light-section method. In the light-section method, light passing through a slit is projected onto a target object to be measured, so as to virtually cut the object using a band-shaped light, and a cut surface is observed in a direction other than the direction of the projected light. Because very fine and intense light beams can be obtained by laser technology, even an object having an irregular surface can be measured at high speed and with high accuracy by employing three-dimensional measurement using the light-section method.
Generally, in the light-section method, the distance to the target object is determined using the principle of triangulation. In triangulation, a triangle is defined by connecting two known reference points and any other third point, and the position of the third point is determined by measuring the angles of the triangle. More specifically, in the light-section method, light which is emitted from a light source within a distance measuring apparatus and passes through a slit is projected onto an object, and the reflected light from the surface of the object is imaged by a CCD camera provided within the distance measuring apparatus. The distance between the distance measuring apparatus and the target object is measured based on the direction of the emitted light and the positions of the light source and the CCD camera. Therefore, it is preferable that the intensity of the reflected light imaged by the CCD camera is constant. Moreover, in the case where the light generated by the distance measuring apparatus is imaged by a CCD camera or the like, it is convenient from the point of image processing, that light which the apparatus has not emitted is not input to the CCD camera. Therefore, in measuring using light, generally an optical filter is used which only passes light of a wavelength of the light emitted by the apparatus, so that light of the surrounding environment is not input.
However, when a floor surface or an obstacle on a floor surface is detected using the light-section method in an optical sensor of a self-controlled mobile robot, if the measurement range of the viewing angle is wider, more candidates can be selected for the movement path. Therefore, it is desirable to use an optical system having a wide viewing angle. On the other hand, an optical filter constituted so as to only pass a specific wavelength band by using interference, has a characteristic in that the pass central wavelength changes according to the incident angle of the incident light.
Therefore if measurement is performed by attaching to an optical system of a CCD camera, an optical filter constituted so as to pass only a wavelength band of laser light generated by the apparatus, the viewing angle becomes narrow. Consequently, the range which can be measured becomes narrow and the path selection process becomes difficult. Furthermore, in the case of imaging laser light generated by the apparatus at a wide angle of view, the pass wavelength band of the optical filter must be made wide. However, if the pass wavelength band is made wide, disturbance light external to the laser light is also imaged. Therefore processing for extracting only laser light from the obtained image must be performed solely by image processing, making the image processing complex. Consequently, this invites a drop in processing speed, and the traveling speed of the self-controlled mobile robot is thus reduced.
In consideration of the above circumstances, an object of the present invention is to provide a distance measuring apparatus and a distance measuring method utilizing a light-section method capable of preventing input of disturbance light without narrowing measurement viewing angle.
A distance measuring apparatus according to the present invention comprises: a laser emitting section for generating laser light, an imaging section for imaging reflected light of the laser light which has been reflected by a surface of a target object to be measured, a telecentric optical system lens for forming an image of the reflected light on the imaging section, an optical filter provided between the telecentric optical system lens and the imaging section and perpendicular to an optical axis of the telecentric optical system lens, for passing only light of a wavelength band of laser light emitted from the laser emitting section, and a distance calculation section for calculating a distance to the object based on an image taken by the imaging section, based on a positional relationship between a light emission position of the laser light and an image position.
In a distance measuring method according to the present invention, laser light is emitted onto a target object to be measured, and laser light reflected by the object is perpendicularly input by an imaging optical system onto an incident surface of an optical filter which passes only light of a wavelength band of the laser light, and the reflected light which has been passed by the optical filter is imaged, and the distance to the object is measured based on the obtained image and a positional relationship between a light emission position of the laser light and the image position.
According to the present invention, in a case where reflected light of laser light such as slit light emitted from an apparatus is imaged, and the distance to an object is measured by referring to a positional relationship between the light emission position of the laser light and the image position, then because the imaging optical system is constructed so that the reflected light is input perpendicular to the incident surface of the optical filter which passes only light of a wavelength band of the laser light emitted by the apparatus, the disturbance light can be removed without narrowing the measurement viewing angle. Furthermore, since in the image to be imaged, only the reflected light of the laser light is included, measurement of the floor surface and recognition processing for an obstacle on the floor surface can be simplified. Moreover, since the disturbance light is removed and recognition processing for an obstacle is simplified, when the present invention is applied to a visual sensor of a self-controlled mobile robot, for example, it is possible to prevent the traveling speed of the self-controlled mobile robot from being reduced.